The present application is based on Japanese Patent Application No. 2001-361721, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of controlling a wiper apparatus for wiping windshield.
2. Description of the Related Art
Recently, for a wiper apparatus for wiping a windshield, a wiper apparatus (an overlap-type wiper apparatus) having configuration that a pair of wiper blades are driven by separate wiper motors and areas which both wiper blades wipe are overlapped in a fixed range has been developed.
FIG. 1 shows the outline of an overlap-type wiper apparatus. As shown in FIG. 1, the overlap-type wiper apparatus is provided with a wiper blade 10 on a driver""s seat side as a first wiper blade and a wiper blade 20 on a passenger seat side as a second wiper blade. Driving force from a wiper motor 11 on the driver""s seat side as a first wiper motor is transmitted to the wiper blade 10 on the driver""s seat side via a link mechanism 12. In the meantime, driving force from a wiper motor 21 on the passenger seat side as a second wiper motor is transmitted to the wiper blade 20 on the passenger seat side via a link mechanism 22.
Normally, the wiper motor 11 on the driver""s seat side is rotated in one direction and the link mechanism 12 converts the rotational driving force to the reciprocative turning operation of the wiper blade 10 on the driver""s seat side. Hereby, the wiper blade 10 on the driver""s seat side is reciprocated between a starting position 2 set on the lower edge of a windshield 1 and a upper return position 3 set on one side edge of the windshield 1.
Similarly, the wiper motor 21 on the passenger seat side is also normally rotated in one direction and the link mechanism 22 converts the rotational driving force to the reciprocative turning operation of the wiper blade 20 on the passenger seat side. Hereby, the wiper blade 20 on the passenger seat side is also reciprocated between a starting position 2 set on the lower edge of the windshield 1 and a upper return position 4 set on the other side edge of the windshield 1.
The reciprocation of each wiper blade 10, 20 is started from each starting position 2, however, to avoid interference between each other, control is made so that one wiper blade 10 or 20 is moved first and the other wiper blade 20 or 10 is moved succeedingly. Generally, for operation from the starting position 2 to the upper return position 3 or 4, the wiper blade 10 on the driver""s seat side is moved first and the wiper blade 20 on the passenger seat side is moved succeedingly. Conversely, for operation from the upper return position 3 or 4 to the starting position 2, the wiper blade 20 on the passenger seat side is moved first and the wiper blade 10 on the driver""s seat side is moved succeedingly.
The wiper blade 10 on the driver""s seat side wipes a first wiped area 1A of the windshield 1 and the wiper blade 20 on the passenger seat side wipes a second wiped area 1B of the windshield 1. These areas 1A and 1B wiped by each wiper blade are set so that they are overlapped in an area 1C hatched in FIG. 1 (hereinafter called an overlap area).
In the overlap-type wiper apparatus having the configuration described above, each wiper motor 11, 21 is controlled so that it is driven in synchronization with each other, however, the wiping speed of each wiper blade 10, 20 may vary unstably due to various external or internal causes such as the dispersion of wiping resistance to each wiper blade 10, 20. In case the wiping speed of each wiper blade 10, 20 varies unstably, it is supposed that the wiper blade moved subsequently catches up with the precedent wiper blade and collides with it particularly in the overlap area.
The invention is made in view of such a situation and the object is to ensure the optimum wiping operation in which relation in order between each wiper blade is maintained and to prevent collision in an overlap area.
In the invention, the wiper apparatus adapted for a vehicle is provided with a first wiper blade for being reciprocated between a first starting position set on a lower edge of windshield and one upper return position set on one side edge of the windshield and wiping a first wiped area of the windshield, a second wiper blade for being reciprocated between a second starting position set on the lower edge of the windshield and the other upper return position set on the other side edge of the windshield and wiping a second wiped area of the windshield, a first wiper blade for driving the first wiper blade and a second wiper motor for driving the second wiper blade and configured so that each wiper blade wipes an overlap area in which the first wiped area and the second wiped area are overlapped in a state in which the wiper blades are overlapped.
In upward operation from the starting position toward the upper return position, the first wiper blade is moved in the overlap area prior to the second wiper blade and in return operation from the upper return position toward the starting position, the second wiper blade is moved in the overlap area prior to the first wiper blade.
The invention is characterized in that an output level of current to each wiper motor is controlled so that at least the following conditions (a) and (b) are met in the wiper apparatus.
(a) An output level of current to the first wiper motor is set to be higher than an output level of current to the second wiper motor when each wiper blade is moved in an area from the starting position to a predetermined first wiping position in the upward operation.
(b) The output level of current to the second wiper motor is set to be higher than the output level of current to the first wiper motor, when each wiper blade is moved in an area from each upper return position to a predetermined second wiping position in the return operation.
As described above, the preceding first wiper blade in the upward operation can be moved faster than the second wiper blade moved succeedingly by setting the output level of current to the first wiper motor to a larger value for a while since the start of the upward operation. The preceding second wiper blade in the return operation can be moved faster than the first wiper blade moved succeedingly by setting the output level of current to the second wiper motor for a while since the start of the return operation to a larger value. As a result, suitable wiping operation in which relation between the preceding and succeeding wiper blades is kept is ensured and the collision in the overlap area can be prevented.
It is desirable that the first wiping position is set in the vicinity of the trailing edge of the overlap area and it is also desirable that the second wiping position is set in the vicinity of the entry edge into the overlap area. The collision of each wiper blade in the overlap area can be more securely prevented by setting as described above.
The invention is further characterized in that the output level of current to each wiper motor is controlled so that the following conditions (c) and (d) are met in addition to the conditions (a) and (b).
(c) The output level of current to the second wiper motor is set to be higher than the output level of current to the first wiper motor when each wiper blade is moved in an area from the first wiping position to each upper return position in the upward operation.
(d) The output level of current to the first wiper motor is set to be higher than the output level of current to the second wiper motor, when each wiper blade is moved in an area from the second wiping position to the starting position in the return operation.
The wiper blade moved succeedingly is faster moved than the preceding wiper blade by controlling the output level of current to each wiper motor as described above and difference in the quantity of relative movement between each wiper blade broadened by the control in the conditions (a) and (b) can be reduced.
The output level of current to each wiper motor can be controlled by a value acquired by dividing the output period of driving voltage output to each wiper motor by an output cycle. The value is called duty ratio and the overlap-type wiper apparatus normally controls the driving of each wiper motor at duty ratio.
Further, the present invention provides a wiper apparatus adapted for a vehicle, comprising:
a first wiper blade for wiping a first wiped area of a windshield, the first wiper blade being reciprocated between a first starting position set on a side of a lower edge of the windshield and a first upper return position set on a side of a first side edge of the windshield;
a first wiper motor for driving the first wiper blade;
a first motor driving circuit for outputting driving voltage input to the first wiper motor so as to rotate the first wiper motor;
a second wiper blade for wiping a second wiped area of the windshield, the second wiper blade being reciprocated between a second starting position set on the lower edge of the windshield and a second upper return position set to a side of a second side edge of the windshield;
a second wiper motor for driving the second wiper blade; and
a second motor driving circuit for outputting driving voltage input to the first wiper motor so as to rotate the first wiper motor;
wherein the first and second wiper blades wipe an overlap area defined by an area on which the first wiped area and the second wiped area are overlapped such that the first wiper blade is moved in the overlap area prior to the second wiper blade in an overlapping manner in an upward operation from the starting positions to the upper return positions respectively, and such that the second wiper blade is moved in the overlap area prior to the first wiper blade in a return operation from the upper return positions to the starting positions,
wherein each motor driving circuit changes a mean output level of current to each wiper motor so that:
(a) an output level of current to the first wiper motor is set to be higher than an output level of current to the second wiper motor, when the wiper blade is moved from the starting position to a predetermined first wiping position in the upward operation; and
(b) the output level of current to the second wiper motor is set to be higher than the output level of current to the first wiper motor, when the second wiper blade is moved from each upper return position to a predetermined second wiping position in the return operation.